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Physical Science EOCT Review

Domain 4: Physics- Waves

Electricity and Magnetism

Domain 3: Physics- Waves

Waves & Sound

A. Waves

1. The nature of waves

a. A wave is a rhythmic

disturbance that transfers energy.

b. All waves are made by

something that vibrates.

2. Mechanical waves need a matter

medium to travel through.

(sound, water, seismic)

3. Two basic types of waves:

a. Transverse

b. Compressional

(longitudinal)

4. Wave properties:

a. Wavelength - distance from a

point on a wave to the same

corresponding point on the next

wave.

b. Frequency - number of waves

that pass a point in one second

(expressed in Hz).

c. Wavelength has an inverse

relationship to wave frequency.

d. Wave velocity depends on the

type of wave and medium.

1) Sound is faster in more

dense media and in higher temps.

2) Light is slower in more

dense media, but faster in a vacuum.

3)

e. Amplitude - size related to the

energy carried by the wave.

1) Transverse - how high

above or how low below the nodal

line.

2) Compressional - how dense

the medium is at the compressions &

rarefactions.

Light• The study of light led to the development of

the quantum mechanical model.

• Light is a kind of electromagnetic radiation.

• Electromagnetic radiation includes many

types: gamma rays, x-rays, radio waves…

• Speed of light = 2.998 x 108 m/s, and is

abbreviated “c”

• All electromagnetic radiation travels at this

same rate when measured in a vacuum

- Page 139

“R O Y G B I V”

Frequency Increases

Wavelength Longer

Parts of a wave

Wavelength

AmplitudeOrigin

Crest

Trough

Equation:

c =λνλνλνλν

c = speed of light, a constant (2.998 x 108 m/s)

νννν (nu) = frequency, in units of hertz (hz or sec-1)

λλλλ (lambda) = wavelength, in meters

Electromagnetic radiation propagates through space as a wave moving at the speed of light.

Wavelength and Frequency• Are inversely related

• As one goes up the other goes down.

• Different frequencies of light are different colors of light.

• There is a wide variety of frequencies

• The whole range is called a spectrum

Radio

waves

Micro

waves

Infrared

.

Ultra-

violet

X-

Rays

Gamma

Rays

Low Frequency

High Frequency

Long Wavelength

Short WavelengthVisible Light

Low Energy

High Energy

Domain 3: Physics- Wave

Interactions

Wave behavior:

a. Reflection - the bouncing back

of a wave.

1) Sound echoes

2) Light images in

mirrors

3) Law of reflection

i = r

b. Refraction - the bending

of a wave caused by a change

in speed as the wave moves

from one medium to another.

The girl sees

the boy’s foot

closer to the

surface than

it actually is.

If the boy looks down at his feet, will

they seem closer to him than they

really are?

No! He is looking straight down and

not at an angle. There is no

refraction for him.

c. Diffraction - the

bending of a wave

around the edge of an

object.

1) Water waves

bending around

islands

2) Water waves

passing through a slit

and spreading out

3) Diffraction depends on the

size of the obstacle or opening

compared to the wavelength of the

wave.

Less occurs if wavelength is smaller than the object.

More occurs if wavelength is larger than the object.

d. Interference -

two or more waves

overlapping to form a

new wave.

1) Constructive (in phase)

Sound waves that constructively

interfere are louder

2) Destructive (out of phase)

Sound waves that destructively

interfere are not as loud

4) AM radio waves are longer

and can diffract around large

buildings and mountains; FM can’t.

5) Ultrasonic sound has a

frequency greater than 20,000 Hz.

a) Dogs (up to 35,000 Hz)

b) Bats (over 100,000 Hz)

c) Medical diagnosis

6) Infrasonic sound has a

frequency below 20 Hz; they are felt

rather than heard

(earthquakes, heavy machinery).

c. Speed of sound

1) 332 m/s in air at 0 C.

2) Changes by 0.6 m/s for every

Celsius degree from 0 C.

3) Subsonic – slower

4) Supersonic – faster than

sound (Mach 1 = speed of sound)

5) Sonic boom (pressure cone)

d. The Doppler effect – the change

in pitch due to a moving wave source.

1) Objects moving toward you

cause a higher pitched sound.

2) Objects moving away cause

sound of lower pitch.

3) Used in radar by police and

meteorologists and in astronomy.

d. The Doppler effect –

the change in pitch due to a

moving wave source.

1) Objects moving

toward you cause a higher

pitched sound.

2) Objects moving

away cause sound of lower

pitch.

3) Used in radar by

police and meteorologists

and in astronomy.

Domain 3: Physics-

Electricity and Magnetism

Charged Particles• Neutrons have no charge

• Neutrons have no effect on the charge

• Charges in objects can produce a force

between the objects

• Objects are forced together or attracted when

their charges are different

• “Opposite charges attract”

• Same electric charges they push apart

• “Like charges repel”

Generating a static discharge

• Electrons can be moved around

• Rubbing fur or cloth against rubber (like a balloon) will move some electrons from the cloth to the balloon

• Both the cloth and the balloon will have a charge.

• What will the charge on the balloon be?

• What will the charge on the cloth be?

Electric Field

• Don’t have to touch to feel a charge.

• An electric field surrounds all charged objects.

• Electric forces act at a distance because or this field.

Static Electricity

• Static means not moving

• Static electricity is electricity at rest

• Friction can cause it

• Objects rub together and electrons move from one object another.

Two ways to move electrons

• Conduction: electrons are transferred by direct contact.

• Induction: electrons on an object are rearranged without physical contact.

Electroscope

No Charge-leaves hang straight down

Induction

Rod with negative charge

Induction

Rod with negative charge

Pushes electrons in electroscope down

Induction

Rod with negative charge

Pushes electrons in electroscope down

Extra negative charge

Induction

Rod with negative charge

Pushes electrons in electroscope down

Extra negative charge

Leaves move apart

Induction

Remove rod everything returns

Conduction

Rod with negative charge

Conduction

Rod with negative charge

Conduction

Rod with negative charge

Transfers electrons

Conduction

Rod with negative charge

Transfers electrons

Extra negative charge

Conduction

Rod with negative charge

Transfers electrons

Extra negative charge Moves leaves apart.

Conduction

Remove rod leaves stay apart.

Static discharge

• Eventually static electric charge will move.

• Slowly the electrons may move into moisture in the air

• Or quickly in a spark.

Two types of materials

• Conductors: a material through which electric charges move easily.

• Metals are good conductors

• Insulators: a material through which electric charges can’t move easily.

• Plastics, rubber, ceramics, wood

Electroscope• Flask

• Metal bar (conductor) through rubber stopper (insulator)

• Two pieces of thin foil on the bottom

• Charge on the metal will push the foil apart

• because they have the same charge

Electricity that moves…

• Current: The flow of electrons

from one place to another.

• Measured in amperes (amps)

• Kinetic energy

How can we control currents?

• With circuits.

• Circuit: is a path for the flow of

electrons. We use wires.

There are 2 types of currents:

• Direct Current (DC) – Where

electrons flow in the same

direction in a wire.

There are 2 types of currents:

• Alternating Current (AC) –

electrons flow in different

directions in a wire

There are 2 types of circuits:

• Series Circuit: the components

are lined up along one path. If

the circuit is broken, all

components turn off.

Series Circuit

There are 2 types of circuits:

• Parallel Circuit – there are several

branching paths to the

components. If the circuit is

broken at any one branch, only

the components on that branch

will turn off.

Parallel Circuit

Ohm’s Law

• Resistance = Voltage / Current

• Ohms = Volts / Amps

Practice with Ohm’s Law

8486

5459

15302

1015015

251004

AmpsVoltsOhms

Domain 3: Physics-

Magnetism

What is an electromagnet?

• Electromagnet – a magnet made

from a current bearing coil of wire

wrapped around an iron or steel

core.

What is a generator?

• Generator – a machine that

changes mechanical energy to

electrical energy

• Usually use moving magnets to

create currents in coils of wire.

What is a motor?

• Motor – a device that changes

electrical energy to mechanical

energy that can do work.